This is an example of a COBOL program and JCL that will create and process a Generation Data Group or GDG on a Mainframe System with ZOS or a Linux. Generation Data Groups (GDGs) are group of datasets related to each other by a common name. The common name is referred as GDG base and each dataset. JCL & VSAM: Hi all, I want to know the major difference between the dataset and GDG. reagrds akshatha.

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We’ll introduce you to the hardware and peripherals. We’ll talk about the operating system, the software installed on a mainframe. We’ll also talk about the different people who work on a mainframe.

JCL Defining Datasets

In a nutshell, we’ll de-mystify the mainframe. Readers based in Indiacan buy the e-book for Rs.

International readers based in the US and other countries can click here to purchase the e-book. Suppose we have stored a large amount of mainvrame of all credit-card holders in a Sequential Dataset.


JCL – Defining Datasets

The Credit-card holders dataset, stores their name, billing address, total credit limit, available balance, minimum amount due etc. The data in the Credit-card holder file has to be updated every to reflect the purchases and payments made by the card-holder.

Suppose, the Credit Card Accounts have been updated till the month of July. In other words, we need to preserve the past historical data.

What if the customer wanted a mainfrake which shows him, his Bank Account Statement of the last 6 months? When we want to maintain not only the current version of the file, but also previous versions, this calls for Generation Data Group GDG.

Concept Solutions Corporation: What are Generation Data Groups (GDG)

If we update this dataset, to create the next generation, the generation number becomes GV Again, for the next generation, the generation number will be GV00, and so on How to access a particular generation?

There are two ways to do this. The other way, we can access generations is by using relative referencing. The current generation is called Generation 0. Thus, we can access datasets within a GDG in 2 ways: The following JCL shows how: Here, we have kept limit as 3.


What is a GDG?

This means, a maximum of 3 generations will be stored in the GDG. You can specify any no.

What is GDG Model? This means, all the generations within the GDG follow, the same record format, the same record length, the same block size etc.

To create a GDG Model, we simply need to create an empty dataset, no maifnrame allocation, and bearing the DCB of the generations, you want to create. Rest all remains the same, just like we create an ordinary dataset. To many people who are thrown to work at a mainframe computer on their first job, they feel lost.

Mainframe people seem to speak a completely different language and that doesn’t make life mainfraem. What’s more, the books and manuals are incredibly hard to comprehend.